Question

Which of the following relations are correct for pressure coefficient?

(a) CP=\(\frac{P}{\frac{\rho n^3D^4}{2}}\)

(b) CP=\(\frac{P}{\frac{\rho n^2D^5}{2}}\)

(c) CP=\(\frac{TV}{\frac{\rho n^3D^5}{2}}\)

(d) CP=\(\frac{P}{\frac{\rho n^3D^5}{2}}\)

I got this question by my college director while I was bunking the class.

My question is based upon Power Producing Power Plant topic in chapter Aircraft Force Systems and the Equations of Motion of Aircraft Performance

Answer 1

Right option is (d) CP=\(\frac{P}{\frac{\rho n^3D^5}{2}}\)

For explanation I would say: The propeller efficiency depends on the propeller advance ratio and power coefficient. The pressure coefficient is given by CP=\(\frac{P}{\frac{\rho n^3D^5}{2}}\) where CP is pressure coefficient, ρ is density, P is shaft power, n is rotational speed and D is propeller diameter. Also propeller advance ratio is given by J= \(\frac{V}{nD}\) where J is propeller advance ratio, V is true airspeed, n is rotational speed and D is propeller diameter.